The Earth Science Picture of the Day (EPOD) highlights the diverse processes and phenomena which shape our planet and our lives. EPOD will collect and archive photos, imagery, graphics, and artwork with short explanatory captions and links exemplifying features within the Earth system. The community is invited to contribute digital imagery, short captions and relevant links.

Encore - Aurora Borealis from Barrow, Alaska

September 16, 2017

Today and every Saturday Earth Science Picture of the Day invites you to rediscover favorites from the past. Saturday posts feature an EPOD that was chosen by viewers like you in our monthly Viewers' Choice polls. Join us as we look back at these intriguing and captivating images.

The photo above shows a bright green aurora commanding the night sky over Point Barrow, Alaska as observed on March 9, 2012 with the camera facing northeast. It was taken during the NASA BRomine, Ozone, and Mercury Experiment (BROMEX). Intense solar storms (solar flares) the first week of March ignited these striking northern lights. High-speed particles (solar wind) generated by solar flares are guided along magnetic field lines as they near the Earth. These particles excite electrons primarily in oxygen and nitrogen atoms of the upper atmosphere above the poles. Oxygen emits most strongly in the green portion (530 nanometers) of the electromagnetic spectrum. In this case it’s mostly the oxygen atoms that have been excited. That’s the Moon, not the Sun, rising over sea ice in the Arctic Ocean.